Power supply circuit



Jan. 15, 1935. w. VAN B ROBERTS 1,987,976

POWER SUPPLY C IRCUIT Original Filed Oct. 26, 1928 INVENTOR W. VAN BROBERTS ATTO R N EY Patented Jan. 15, 1935 UNITED STATES PATENT OFFICEPOWER SUPPLY CIRCUIT Walter van B. Roberts. Princeton, N. 1., alaignorto Radio Corporation of America, a corporation of Delaware 7 Claims.(Cl. zso-z'n This invention relates, broadly to a means for maintaininga constant current in a circuit that is subject to current and voltagepulsations. More particularly, this invention relates to circuits such 3as a power supply circuit for a radio receiving set, and to means formaintaining a constant current in such a circuit.

It is well known to form a power supply circuit from a means forrectifying alternating current and a filter circuit comprisingcondensers and choke coils for smoothing out the rectified current. Goodresults and a practically constant current can be obtained in the outputof such power supply circuits when large and relatively expensive chokecoils and condensers are used in the filter circuit. In many instances,however, it is desirable to use small and inexpensive choke coils andcondensers and in such instances, a slightly pulsating current isobtained in the output. My invention relates to a means for eliminatingsuch pulsations.

It is the object of my invention to provide I means for maintaining aconstant current in any circuit that is subject to current and voltagepulsations.

It-is a further object of my invention to place the equivalent of abalancing voltage in a circuit and to vary this voltage by means of thepulsations which it is desired to eliminate.

It is a further object of my invention to connect a space dischargedevice in series in a circuitwhich is subject to current and voltagepulsations and to vary the effective resistance of the space dischargepath of said space discharge device in order to eliminate or reduce saidpulsations to a minimum.

It is a still further object of my invention to provide means in placeof or in addition to the choke coils and condensers of the filtercircuit, for obtaining a relatively smooth current output in a powersupply circuit.

Other objects of my invention will become apparent upon reading thespecification and appended claims of this application which is adivision of my copending application filed October 26, 1928, Serial No.315,142, Patent No. 1,925,569 Sept. 5, 1933.

These objects of my invention are attained by including a spacedischarge device in the circuit to be controlled, and by providing meansfor instantaneously varying the effective impedance of the spacedischarge device in accordance with the pulsations to be controlled.That is, means are provided for varying the apparent or effectiveresistance of the space discharge path of the device with respect to thecurrent pulsations or tending to pass therethr h.

In the case .of the power pply circuit, a space discharge device such asordinary threeelectrode thermionic valve is connected in series in saidcircuit so that the circuit is completed by the space discharge path ofthe space discharge device. It is to be understood that the valve willpass suilicient current for the proper operation of the radio receivingset. Means are provided and associated with said space. discharge devicefor impressing upon the control grid thereof a potential which is 180out of phase with the voltage pulsations in the power supply circuit.

The means which may comprise a transformer connected across the outputof the filter section of the power supply circuit, is such that thereverse potential applied to the control grid of the space tischargedevice, has a value substantially equal times the value of the voltagepulsations in the power supply circuit where a is the amplificationconstant of the valve. As a result the equivalent of a balancing voltageis introduced into the circuit, or looked at from a slightly differentpoint of view, the efiective resistance of the space discharge path ischanged in such a manner that the current through the space dischargedevice which is incidentally the current in the output of the powersupply circuit, remains constant regardless of the potential variationstending to pass more current through the circuit.

The details of an approved form of my invention will be more readilyunderstood by referring to the following specification which should beread in connection with the accompanying drawing in which the singlefigure illustrates diagrammatically a power supply circuit which hasbeen modified according to my invention.

The accompanying drawing illustrates an application of my invention to apower supply circuit such as is used for supplying power to operate aradio receiving circuit. In this power supply circuit a transformerwhose primary winding is adapted to be connected to the localalternating current mains, has its secondary winding connected to arectifying means 31. The member 31 is shown as a whole wave rectifier ofthe heated cathode type but it is to be understood that any other typeof rectifying means can be used equally well. The cathode of therectifier is preferably heated from a separate winding on the 2transformer 30. A connection 32 to the cathode of the rectifier, and asecond connection 33 to the midpoint of the secondary winding of thetransformer 30, form respectively the positive and negative side of thecircuit.

A choke coil 34 is inserted in the circuit, and two condensers 35 and 36are shunted across the circuit on each side of the choke coil to smoothout the current and voltage pulsations. A resist ance member 37 isshunted across the circuit and various taps 38 are provided on theresistance member for obtaining the desired potential drop for thevarious operating needs of the receiving circuit. All of this structureso far described is well known in the art and various substitutions canbe madefor parts of this structure without changing the general natureof the power supply circuit. A" power supply circuit, as described,provides a relatively smooth current only when large and expensive chokecoils and capacities are employed. Otherwise objectionable current andvoltage pulsations are present in the output of the power supplycircuit.

According to my invention a space discharge device 39 of the threeelement type, is inserted in the power supply circuit, so that thecircuit is completed by the space current of the device. According tothe broad principle of my invention, the space current of the device 39is kept constant and the objectionable pulsations are thereforeprevented from passing through the resistance member or voltage divider37.

The constant space current maybe obtained by impressing upon the grid ofthe device 39 a potential which is 180 out of phase with the ob-Jectionable pulsations and which has a magnitude equal substantially totimes the magnitude of the pulsations. In the modification illustrated Iaccomplish this by connecting a series arrangement comprising acondenser 40 and a primary winding 41 across the power supply circuitand by coupling a secondary winding 42 to the winding 41. The condenser40 is provided so that only the alternating component of the current inthe power supply circuit will pass through the winding 41. The grid ofvalve 39 is connected to the winding 42, preferably by a slide member 43so that the potential impressed upon the grid has the proper magnitude.The reverse potential is obtained by winding the coils 41 and 42 inopposite directions and the windings should be such that a tightcoupling is obtained between these coils. A resistance 44 is provided tomaintain the desired grid bias.

The cathode of the device 39 can be heated by alternating current from awinding on the transformer 30 or by any other means. Connections couldalso be made to obtain thev cathode heating current from the resistancemember 37 but in that case it would benecessary to provide a temporarycircuit shunting the anode and cathode to complete the power supplycircuit and cause a flow of current through resistance 37 until thecathode had heated sufiiciently for the device to pass current. Such ashunting circuit 45 containing either an automatic or a manuallyoperated switch 46 could also be used to complete the power supplycircuit in the case of emergency such as the buming out of the device39. The shunting circuit 45 contains a resistance 47 equal to theapparent resistance of the device 39.

In the operation 01 a power supply circiut modified in accordance withmy invention, when there is an increase in the potentialin the circuittending to increase the space current of the device, a negativepotential of the proper magnitude is impressed upon its grid to vary theefiective impedance of the space discharge path and thus maintain aconstant space current and consequently a constant current through theresistance 37.

Various other modifications of the circuits disclosed and various otherapplications of the broad principle of my invention have beencontemplated by me and I do not intend to be limited by themodifications disclosed but only by the scope of the appended claims.

I claim:

1. In a power supply circuit, a source of fiuctuating energy, a voltagedividing member and a variable impedance device forming a series circuitconnected across said source, a control element for said variableimpedance device, a second circuit connected across said source andmeans for causing said control element to function in response tofluctuations of energy flowing in said second circuit, and meanscontrolled thereby for maintaining the voltage across said voltagedividing member substantially constant.

2. A power supply circuit comprising means for rectifying alternatingcurrent, a filter circuit for smoothing out the rectified current, adirect cur-' rent path consisting of a voltage dividing resistancemember and a space discharge device convoltage dividing resistancemember and a triodeconnected in series across the output of said filtercircuit, said triode containing an anode, a cathode, and a controlelectrode, said anode being connected through said resistance member tothe positive side of said filter circuit and said cathode beingconnected to the negative side of said filter circuit, a transformerhaving primary and secondary windings, a condenser and said primarywinding connected in series across the output of said filter circuit,said secondary winding being connected between said cathode and saidcontrol electrode, a resistance included in the connection between saidcathode and said control electrode, and a switch for by-passing currentaround said triode.

4. A power supply circuit comprising means for rectifying alternatingcurrent, a filter circuit for smoothing out the rectified current, saidfilter circuit being adapted to have a pulsating current in its output,and a pair of paths connected in parallel across the output of saidfilter circuit, one of said paths including means for preventing thedirect current component of said pulsating current from passingtherethrough and-the other of said paths including means for preventingthe alternating current component of said pulsating current from passingtherethrough;

5. A power supply circuit comprising means for rectifying alternatingcurrent, a filter circuit circuit being adapted to have a pulsatingcurrent in its output, and a pair of paths connected in parallel acrossthe output of said filter circuit, one of said paths including means forpermitting only the alternating current component oi said pulsatingcurrent to pass therethrough, and the other of sgid paths includingmeans for permitting only is e direct current component 0! saidpulsating current to pass therethrough, said last mentioned meanscomprising a variable impedance member whose impedance is controlled bythe alternating current component in said first mentioned path.

6. A power supply system comprising a source of fluctuating directcurrent, a pair of paths connected in parallel across the output of saidsource, one of said paths including means for permitting only thealternating current component of said fluctuating current to passtherethrough, the other of said paths including means for permitting thedirect current component of said fluctuating current to passtherethrough said last mentioned means comprising a variable impedancemember whose impedance is controlled by the alternating currentcomponent in said first mentioned path.

'7. A power supply system comprising a source oi fluctuating current apair of paths connected in parallel across said source, one of saidpaths including means for permitting only the alternating currentcomponent of said fluctuating current to pass therethrough, the other ofsaid paths including means for permitting the direct current componentof said fluctuating current to pass therethrough, said last mentionedmeans comprising a space discharge device the output circuit of which isincluded in said direct current path and the input circuit of which isconnected to said alternating current path.

WALTER van B. ROBERTS.

